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- /*
- Technitium DNS Server
- Copyright (C) 2024 Shreyas Zare (shreyas@technitium.com)
- This program is free software: you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation, either version 3 of the License, or
- (at your option) any later version.
- This program is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
- You should have received a copy of the GNU General Public License
- along with this program. If not, see <http://www.gnu.org/licenses/>.
- */
- using DnsServerCore.ApplicationCommon;
- using System.Collections.Generic;
- using System.IO;
- using System.Net;
- using System.Text.Json;
- using System.Threading.Tasks;
- using TechnitiumLibrary;
- using TechnitiumLibrary.Net;
- using TechnitiumLibrary.Net.Dns;
- using TechnitiumLibrary.Net.Dns.ResourceRecords;
- namespace DnsRebindingProtection
- {
- public sealed class App : IDnsApplication, IDnsPostProcessor
- {
- #region variables
- bool _enableProtection;
- NetworkAddress[] _bypassNetworks;
- HashSet<NetworkAddress> _privateNetworks;
- HashSet<string> _privateDomains;
- #endregion
- #region IDisposable
- public void Dispose()
- {
- // Nothing to dispose of.
- }
- #endregion
- #region private
- private static string GetParentZone(string domain)
- {
- int i = domain.IndexOf('.');
- if (i > -1)
- return domain[(i + 1)..];
- //dont return root zone
- return null;
- }
- private bool IsPrivateDomain(string domain)
- {
- domain = domain.ToLowerInvariant();
- do
- {
- if (_privateDomains.Contains(domain))
- return true;
- domain = GetParentZone(domain);
- }
- while (domain is not null);
- return false;
- }
- private bool IsRebindingAttempt(DnsResourceRecord record)
- {
- IPAddress address;
- switch (record.Type)
- {
- case DnsResourceRecordType.A:
- if (IsPrivateDomain(record.Name))
- return false;
- address = (record.RDATA as DnsARecordData).Address;
- break;
- case DnsResourceRecordType.AAAA:
- if (IsPrivateDomain(record.Name))
- return false;
- address = (record.RDATA as DnsAAAARecordData).Address;
- break;
- default:
- return false;
- }
- foreach (NetworkAddress networkAddress in _privateNetworks)
- {
- if (networkAddress.Contains(address))
- return true;
- }
- return false;
- }
- private bool TryDetectRebinding(IReadOnlyList<DnsResourceRecord> answer, out List<DnsResourceRecord> protectedAnswer)
- {
- for (int i = 0; i < answer.Count; i++)
- {
- DnsResourceRecord record = answer[i];
- if (IsRebindingAttempt(record))
- {
- //rebinding attempt detected!
- //prepare protected answer
- protectedAnswer = new List<DnsResourceRecord>(answer.Count);
- //copy passed records
- for (int j = 0; j < i; j++)
- protectedAnswer.Add(answer[j]);
- //copy remaining records with check
- for (int j = i + 1; j < answer.Count; j++)
- {
- record = answer[j];
- if (!IsRebindingAttempt(record))
- protectedAnswer.Add(record);
- }
- return true;
- }
- }
- protectedAnswer = null;
- return false;
- }
- #endregion
- #region public
- public async Task InitializeAsync(IDnsServer dnsServer, string config)
- {
- using JsonDocument jsonDocument = JsonDocument.Parse(config);
- JsonElement jsonConfig = jsonDocument.RootElement;
- _enableProtection = jsonConfig.GetPropertyValue("enableProtection", true);
- _privateNetworks = new HashSet<NetworkAddress>(jsonConfig.ReadArray("privateNetworks", NetworkAddress.Parse));
- _privateDomains = new HashSet<string>(jsonConfig.ReadArray("privateDomains"));
- if (jsonConfig.TryReadArray("bypassNetworks", NetworkAddress.Parse, out NetworkAddress[] bypassNetworks))
- {
- _bypassNetworks = bypassNetworks;
- }
- else
- {
- _bypassNetworks = [];
- //update config for new feature
- config = config.Replace("\"privateNetworks\"", "\"bypassNetworks\": [\r\n ],\r\n \"privateNetworks\"");
- await File.WriteAllTextAsync(Path.Combine(dnsServer.ApplicationFolder, "dnsApp.config"), config);
- }
- }
- public Task<DnsDatagram> PostProcessAsync(DnsDatagram request, IPEndPoint remoteEP, DnsTransportProtocol protocol, DnsDatagram response)
- {
- // Do not filter authoritative responses. Because in this case any rebinding is intentional.
- if (!_enableProtection || response.AuthoritativeAnswer)
- return Task.FromResult(response);
- IPAddress remoteIP = remoteEP.Address;
- foreach (NetworkAddress network in _bypassNetworks)
- {
- if (network.Contains(remoteIP))
- return Task.FromResult(response);
- }
- if (TryDetectRebinding(response.Answer, out List<DnsResourceRecord> protectedAnswer))
- return Task.FromResult(response.Clone(protectedAnswer));
- return Task.FromResult(response);
- }
- #endregion
- #region properties
- public string Description
- { get { return "Protects from DNS rebinding attacks using configured private domains and networks."; } }
- #endregion
- }
- }
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